Marine current power generation is expected to provide a relatively uniform and predictable output, compared with other power generations such as wind power generation and solar power generation that tend to provide a fluctuating output. Thus, the marine current power generation devices are developing. For example, a bulb-type power generation device is known that has a drive power transmission mechanism and a power generator in a bulb.
This is because the marine current power generation device is placed in the sea or at the bottom of the sea where the speed of the tide is fast, and should be able to supply a stable electricity, its drive power transmission mechanism desirably has a long life and high reliability and is desirably maintenance free.